Coal can clean up its act
For critics of coal – and there are many – it is an archaic fuel with no place in the future. Images of smog-filled skies above China and increasingly India, two of the world’s largest users, have shown just how bad the pollution from coal plants can be.
Dubai, however, has committed itself to “clean coal” and is seeking out the latest technology for its Hassyan coal power plant.
Dubai Electricity and Water Authority (Dewa) is in the final stages of awarding a tender for the 1,200-megawatt coal plant. The Hassyan project is part of a plan to diversify the UAE’s energy mix by 2030 to comprise 71 per cent natural gas, 12 per cent nuclear power, 12 per cent “clean coal” and 5 per cent solar power.
In January the managing director and chief executive of Dewa, Saeed Mohammed Al Tayer, described the Hassyan project as a key step in the implementation of the energy diversification strategy formulated by the Dubai Supreme Council of Energy, to introduce clean coal-based electricity generation into Dubai’s energy mix.
The idea that coal can be clean is greeted with scepticism by environmentalists but the technology exists – it simply hasn’t been widely adopted yet, for reasons relating to cost and the conservative nature of most utilities when faced with change.
“Coal power plants are being built the same today as they were 70 years ago,” says Mohamed Belaid, senior lecturer and a researcher in the engineering faculty at the University of Johannesburg.
South Africa is currently building the world’s biggest dry-fired coal plant, and draws about 95 per cent of its energy from coal. It is also one of the largest exporters of the fuel, so interest in alternative ways of using it as an energy source runs deep. (A dry-fired coal plant cools the coal without using water.) “Conventional plants use pulverised coal that is blasted into a boiler. The gases escape into the atmosphere, where they form sulphuric acid – or acid rain. These contaminants can be removed, by adding a flue gas desulphurisation plant,” Mr Belaid says.
This costly process is one most utilities go a long way to avoid. Besides, it would be better to remove carcinogens before they escape, Mr Belaid says.
Instead, he advocates using a process called circulating fluidised bed technology (CFB). This technology has the ability to capture sulphur dioxide (SO2) gas. It uses limestone injected into the furnace. The calcium in the limestone combines with SO2 to form solid material that falls to the bottom of the chamber, from where it can be removed.
“This can reduce the emission of SO2 up to 90 per cent of harmful components,” says Mr Belaid.
A CFB plant is already in operation at Lagisza, Poland. Others have been commissioned in China and South Korea. At least one is planned for South Africa.
Still, clean coal projects are relatively rare, and it will be interesting to see what technology Dubai settles on. Whatever option it chooses, the emirate has the potential to participate as a leader in the use of clean coal.
Dubai will be also relatively unique in another aspect – it has no coal reserves of its own and will have to find supplies on the international market. Similar to oil refineries, which are designed to run on specific grades of crude, traditional coal plants are designed to accommodate a specific grade, or thermal range, of fuel. A dizzying variety of grades exists, based on the heat it will potentially produce.
Conventional coal boilers are specially designed for a certain type of fuel. A plant set up to run on lower grades that produce less heat, cannot burn higher grade coals that run hotter. There are many other factors that affect the type of coal fed into pulverised coal-fired boilers, which affects efficiency. Fluidised bed technology however offers a good solution regarding flexibility. It can burn any grade of coal including coal refuse, petroleum coke and biomass without significant modifications.
These newer plants can keep operating regardless of coal quality, and in some cases, don’t need to burn only coal. Namibia recently refurbished its ageing Van Eck coal plant and converted it to run partially on brush, mostly harvested invasive plant life that threatens water supplies.
This brush is made into pellets that are fed into the boilers, reducing the amount of coal needed by about a quarter without a drop in power output.
The fuel flexibility of a clean coal plant means it can obtain product from almost anywhere in the world. And it is a big, big supply. The World Coal Association says there are 861 billion tonnes of proven reserves worldwide. Coal can be found on all the major land masses with the biggest reserves in the US, Russia, China and India.
It’s something of a quirk of geology that the Middle East is one of the few significant parts of the world that has negligible amounts of it.
Elsewhere there is so much of it that the coal price has plunged to historic lows. From a peak of about $200 a tonne in 2008, it is now trading at between $55 to $65 a tonne, depending on the grade.
Ultimately coal can provide a reliable addition to Dubai’s base load power without being particularly costly. And with the right technology, the overcast and heavily polluted skies we have seen over China’s cities can be avoided.
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Published: April 25, 2015 04:00 AM